Saudi authorities arrested human rights activist Mayya Al-Zahrani hours after she expressed her shock at the arrest of fellow female activist, Nouf Abdulaziz Al-Jerawi on social media.
Saudi human rights group ALQST confirmed Al-Zahrani's arrest on Twitter.
Al-Jerawi was arrested on Wednesday after posting online that she was a good citizen who helped the oppressed voluntarily by connecting them with lawyers and human rights organisations.
Human rights activist Yahya Assiri said the Saudi policy of arresting activists is similar to Israel's policies against the Palestinians adding that Saudi is still carrying out arrests despite all the international pressures.
The policy will fail, Assiri warned, as Saudi cannot deceive the whole world "no matter how Saudi authorities try to silence people by arresting activists".